Piling

ABSTRACT

A concrete pile fitted with a special slightly tapered concrete tip of larger area. The tip has a central stub with an open socket for receiving concrete poured in after the pile is in place.

United States Patent [191 Merjan PILING [76] Inventor: Stanley Merjan,16 Beacon Dr., Fort Washington, NY. 11050 [22] Filed: Mar. 17, 1972 [21]Appl. No.: 235,790

Related US. Application Data [63] Continuation-impart of Ser. No.97,997, Dec. 14,

[51] Int. Cl. E02d 5/30, E02d 5/48, E08d 5/50 [58] Field of Search...61/53, 53.5, 53.52, 61/56, 56.5, 53.70, 53.72; 52/170, 297

[56] References Cited I UNITED STATES PATENTS 1,778,925 10/1930 Thornley..61/56.5

[ Aug. 14, 1973 Construction Methods & Equip, May 1957, pp. 218, 219,221, 222.

Primary Examiner-Jacob Shapiro Attorney-Abner Sheffer ABSTRACT Aconcrete pile fitted with a special slightly tapered concrete tip oflarger area. The tip has a centra1 stub with an open socket forreceiving concrete poured in after the pile is in place.

20 Claims, 11 Drawing Figures PATENTEI] M19 4W5 SIEEIIOFZ HAMMazlPIlLING This application is a continuation-in-part of my US. Pat.application Ser. No. 97,997 filed Dec. 14, 1970, whose entire disclosureis incorporated herein by reference.

This invention relates to piling.

In present commercial practice, when bedrock is at a reasonable depth,high-capacity H pile steel sections, or open end or closed end pipe canbe driven economically to capacities in excess of 100 tons. Compactsands and stiff clays will generally support I-I pile, steel pipe,mandrel-driven shell type .piles, or pre-cast concrete pipe piles forcapacities in excess of 50 tons and these piles are economical when thelengths are moderate.

However, there are situations where the soil conditions will notconveniently accommodate these specific piling types. For example along,and near, the sandy ocean beaches there are often great depths ofrelatively loose cohesionless materials. l-Iere conventional piles mustpenetrate considerable distances to develop acceptable capacities byfriction forces between the pile surface and the soil. In anothersituation, a thin layer of the relatively loose cohesionless material(usually situated underneath a non-bearing layer of silt, clay or fillor mixtures thereof) overlays a deep stratum of soil of very low bearingcapcity such as soft clay. Here, when the pile is driven through thelayer of loose material it must then be driven through the deep clayeylayer to an acceptable bearing layer below the clay.

The piles of this invention are particularly suitable for use insupporting heavy loads on land in which the bearing soil iscomparatively loose and granular, and not capable of sustaining highunit loads (e.g. soil of N value less than 30, say about five to whichsoil may be situated below a relatively thick layer of soil unsuitablefor bearing such as a fill or soft clay. In such cases it has beenproposed to use a Franki type of pile, in which a mushroom base ofconcrete is pushed out at the bottom of the pile after the pile has beendriven down to the bearing layer. Such piles are described at, forinstance, pages 250- 1 of the book Pile FoundationsTheory-Design-Practice by Robert D. Chellis, published 1951 byMcGraw-Hill, which also discusses a great many other types of pilesknown to the art. As pointed out by Chellis the Franki piles are ofparticular advantage where a bearing stratum, of limited thickness only,can be reached within economical depths. While such Franki piles have,in many cases, large capacities (e.g. 120 tons per pile), theirinstallation is quite complicated and very expensive; special costlyequipment is needed and conventional automated piledriving techniquescannot ordinarily be used. In addition the character of any individualdriven pile is not readily predictable; I believe that this may be due,for instance, to eccentricities in the shape of the mushroom base ofconcrete that is rammed out of the bottom of the pile, and otherfactors.

Among the other piles which are in present commercial use in the loosesoil conditions are the Raymond piles described on pages 233-235 of theChellis book and the Monotube composite tapered pile which typically hasa fluted heavy gauge shell which tapers down. at its base. Where theloose granular soil layer is of limited thickness such piles tend topenetrate through that layer without attaining high capacities and mustthen be driven to considerable depths; even then the capacities do notapproach those attainable using the piles of the present invention.

In accordance with one aspect of this invention there is provided a muchless expensive pile, which can be installed economically withconventional automated techniques and which has high load bearingcapacity in the soil conditions described above. Although the rated loadbearing capacity of my new pile may be below that of a properlyinstalled Franki pile, it is much higher than that of other conventionalpiles. The economy of installation makes it practical to overcome thislower bearing capacity by driving more of my new piles, so that thetotal cost for properly supporting a given building or other structurewill be considerably lower when my new piles are used than when Frankipiles are employed. The construction of my new pile is such that it canbe driven rapidly, accurately, and easily, with good rigidity andstability of direction, by conventional automated pile driving hammersat high impact frequencies (e.g. 50 to 120 blows per minute usingconventional hammers such as described at pages -72 of the Chellis book,the pile driving energy usually being in the range of about 15,00036,000 foot pounds per blow).

Certain preferred forms of the invention are illustrated in theaccompanying drawings in which FIG. 11 is a cross-sectional view, toscale, of one preferred type of pile tip in accordance with thisinvention.

FIG. 2 is a bottom view of the pile tip of FIG. ll.

FIG. 3 is a top view of the pile tip of FIG. I.

FIG. 4 is aside view, also in cross-section, showing the pile tip ofFIG. I connected to the stem of the pile and showing the pile beingdriven into the ground with a removable mandrel housed in a socket inthe pile tip.

FIG. 5 is a side view, also in cross section, of a por' tion of the tipand the lower portion of the pile stem after concrete has been pouredinto the stem.

FIG. 6 is a cross-sectional view, to scale, of another form of pile tipin accordance with this invention, showing the pile tip connected to thetubular stem of the pile.

FIG. 7' illustrates schematically one way of driving the pile shown inFIG. 6.

FIG. 8 illustrates schematically another way of driving the pile shownin FIG. 6.

FIG. 9 is a side view, in cross section, of a portion of the tip of FIG.6 and the lower portion of the pile stem after concrete has been pouredinto the stem.

FIG. 10 is a side view of the invention using a pile tip without asocket.

FIG. 1111 is a view of an arrangement employing a tip having a sleevewhich does not project above the top thereof.

Turning now to FIG. ii the tip ll 1 is of reinforced concrete ofsymmetrically tapered frusto-conical construction with its base 12 beingsubstantially flat (and in a plane substantially perpendicular to theaxis 13 of the tip). The taper is gradual; in FIG. II it is aboutone-half inch per foot. The concrete tip is formed by casting in placearound a relatively short length or stub of threaded (corrugated) steelshell 114 of conventional type leaving a substantially cylindricalcenter open socket 16 in the upper part of the concrete of the tip, andwith a portion 117 of the stub projecting above the substantially flattop surface 18 of the concrete tip.

In FIG. I the reinforcement of the concrete is constituted by a seriesof equally spaced axially oriented reinforcing bars 19 disposed aroundthe socket l6 and extending below the level of the base of the socket,the bars 19 being tied together by transverse reinforcing rods or bars21 secured to bars 19 as by suitable means, e.g. wires ties around thebars. Instead of, or in addition to, reinforcing rods, the concrete maycontain pieces of sheet metal distributed therethrough.

In use, the tip 11 is connected to the stem 22 (FIG. 4) of the pile by asuitable connection, such as a threaded adapter 23, also of conventionalshell construction, engaging both the projecting portion of the stub 14and said stem. A mandrel 24 is disposed within the socket l6 (resting ona steel plate or boot which forms the base 26 of the socket this platepreferably has a larger diameter than that of the stub and is put inplace before the concrete of the tip is cast) for receiving the blow ofthe pile-driving hammer and transmitting its downward force to theconcrete tip. The particular conventional mandrel shown in FIG. 4extends the whole length of the stem. In FIG. 4 the upper portion isshown on a reduced scale and part of the lower portion is broken away toshow details of the mandrel.

As the pile is driven, the tip penetrates through the non-bearing soil,until it reaches the bearing soil. Continued driving forces it into thelatter, generally until the resistance to the driving force indicatesthat there is adequate load bearing capacity (e.g. using standardpile-driving formulas which relate load-bearing capacity to drivingresistance and/or using actual static load tests in which the pile isloaded with twice the load it is expected to carry and the movement ofthe pile under such loading is measured, a movement of about one inch orless in this test generally being an indication that the pile will besatisfactory to carry the expected load).

The mandrel 24 may be of conventional construction. For instance it maybe of the type having a pair of almost hemicylindrical halves 27 which,in use, are pressed apart against the internal walls of the shell (inthis case, including the section of shell lining the socket 16). To thisend there is an inflatable element 28 to which air (or other fluid) isadmitted under pressure so as to expand the element 28 against theinwardly facing walls of the mandrel halves 27. When the mandrel is tobe removed from the socket, the pressure in the inflatable element isreduced and the mandrel halves move together, away from the walls of theshell, under the influence of springs 29 mounted on rods 31 which passthrough the mandrel halves; one end of each spring engages a wall of amandrel half 27 while the other end is held at the outer end of its rod.

Another conventional type of mandrel which may be used is simply a heavypipe extending through the stem and into the socket and resting on thebase of the socket. For instance when the stem and socket each have aninternal diameter of 13 inches, the mandrel may be a l2- /4 inch outsidediameter heavy-walled pipe which is driven by the hammer and transmitsthe driving force to the base 26 of the socket.

After removal of the mandrel, the shell (including the stub and the mainstem of the pile) is filled with concrete. As shown in FIG. the concretefills the socket, making for an excellent connection between tip andstem so that they behave more as an integral unit even in response totension forces. If desired, reinforcement, such as reinforcing rods 32,may be placed so as to extend from the cavity up into the stem beforethe concrete is poured.

In the tip illustrated in FIGS. 6 to 9 the stub 34 is a short piece ofpipe, e.g. straight-sided steel pipe having a diameter of about 8 to 14,or even 18, inches and having a wall thickness of about 0.17 to 0.4 inchor more; the tubular material conventionally used for pipe piles may beused. It is adapted to be joined to the stem 36 of a pipe pile by aconnector, such as an internally tapered sleeve 37 whose internaldiameter is about the same as the external diameter of the stub andstem, there being a drive fit between the sleeve 37 and the top of thestub and between the sleeve and the bottom of the stem; this connectionmay be formed by welding if desired. To assist in anchoring the stub inthe concrete of the tip the stub of FIG. 6 may have welded to its base aflat transverse plate 38 of larger area than the cross-sectional area ofthe stub. This plate (e.g. of V2 inch thick steel) may be welded to thestub before the concrete of the tip is cast. The pile may be driven bypile-driving hammer blows at the top of the stern (FIG. 7) or,particularly when a thin-walled stem is used (which stem may even be ofcorrugated construction), it may be driven by such blows applied to aninternal mandrel 24 (FIG. 8) in the socket 39 formed inside the stub 34.The plate 38 also helps to distribute the vertical pile driving forcesmore uniformly through the concrete tip. When the concrete is pouredinto the stem 36 it fills the socket 39, as shown in FIG. 9; here againreinforcement may be placed so as to extend from the cavity up into thestem.

The particular tips shown in the drawing are designed for use with astem having a diameter of about 12 inches (for the embodiment of FIG. 6)or 14 inches (for the embodiment of FIG. 1). The base 12 of the tip hasa diameter of about 24 inches, which is considerably larger than that ofthe stem. The maximum diameter of the tip, at the top, is about 30inches and the axial height of the tip, measured from its base to thelevel at which its diameter attains its maximum, is about inches, sothat its taper is about three-fifths inch per foot.

In general, tips of this invention may be used with stems of about 8 to18 inch diameter. The tip is preferably circular in cross section(although other crosssections adapted to give a substantially uniformload distribution around the pile, e.g. square cross section, may beemployed) and its projected area (at its maximum diameter) is abovetwice, and preferably about 5 to 15 times, the cross-sectional area ofthe stem. Peferably the base of the tip has a diameter of at least 8inches, although the use of pointed tips is also within the broaderscope of this invention. Preferably the axial height of the tip is atleast two feet and at least 1 foot greater than the depth of the socketbut less than onehalf, more usually less than one-third, of the overallheight of the pile (including the stem). The taper is generally lessthan 3 inches per foot (and preferably less than 1% inches per foot) andabove one-fourth inch per foot (but it is within the broader scope ofthe invention to use an untapered tip). The depth of the socket isgenerally within the range of 1/10 to 9/10 of the axial height of thetip, preferably at least threetenths and less than seven-tenths of thatheight, more preferably about 0.4 to 0.6 times the height of the tip.

The use of the tip of this invention enables one to use shorter lengthsof pile for a given load bearing capacity. Generally the overall lengthof the pile (including tip) will be in the range of about 10 to 50 feetor more.

The ground-engaging surfaces of the concrete tip may be smooth ortextured (e.g. corrugated).

The N value, previously mentioned, is a conventional reference for soilcompactness. It is the number of blows of a 140 lb. hammer, dropped froma height of 30 inches, required to advance a standard 2 inch diametersplit spoon sampling tube a distance of 12 inches.

When the tip is driven through certain non-bearing soils, the soil doesnot flow back around the stem above the tip and there is an unfilledspace around the stem. This space is preferably filled in, from the top,by dumping or otherwise placing material such as sand which may beapplied dry or with water (e.g. it may be puddled or jetted in).

It is also within the broader scope of the invention to use a pile tipwithout a socket. For instance, as illustrated in FIG. the tip 51 mayhave an upper plate 52, to which are welded downwardly extendingreinforcing rods 53 (or other suitable anchoring means) around which theconcrete 54 of the tip is cast, with the concrete being in contact withthe lower face of the plate 52. A stub 56 (which may be a short lengthof pipe of the type used in the embodiment shown in FIG. 6) is welded tothe top of the plate (either before or after the concrete of the tip iscast) to provide an attachment to the stem 57 of the pile. After drivingthe stem and stub are filled with concrete, as previously described.

While the tip of this invention is particularly suitable for use whenattached to the longer stem of a pile, it is also within the broaderscope of this invention to use the tip with a very short stem, orwithout any stem at all, as in situations in which piles or other drivenelements have not been previously employed. For example, when thebearing soil (eg a fine to medium sand of N value about 8 to 10) is at,or very near, the surfaceand is not overlaid by other non-bearing strataof significant thickness, the tip itself (without a stern) may be drivendirectly into the surface, e.g. the tip illustrated in FIG. 1 may bedriven some 6 feet into the soil by means of a conventional pile drivinghammer operating on a mandrel within the socket of the tip. A spacedseries, of such driven tips (the axes of adjacent tips being spacedapart by a distance equal to say about 1% times the largest diameter ofthe tip) can support a heavy building or other structure without theneed for extensive excavation and without the need for large footings ormat foundations.

Instead of using a projecting stub for lining the socket of the concretetip, one may employ a sleeve which does not project above the top of theconcrete tip and which is adapted to be connected to the stem of thepile. In one suitable construction, illustrated in FIG. 1 1, this sleeve61 is made of corrugated shell material of slightly larger diameter thanthe shell material of the pile stem 62 so that, after the tip has beenfabricated and is ready for use, the stem can be attached to the tip byscrewing it into the sleeve 61.

The present invention makes it possible for relatively large volumes ofconcrete, comparable to the volumes of extruded material in Frankipiles, to be more economically put in place in deeper strata and withmore uniform results. As with the Franki piles, the piles of the presentinvention give their results largely by the compaction of the soil oflow bearing value and they attain very highload bearing capacity inrelatively shallow strata. Typical examples of such conditions are asfollows: (a) 18 feet of miscellaneous fill and gray clayey organic siltoverlying a foot thick layer (of N value about of fine silty sand(containing some medium gravel) overlying more than 50 feet of clay; (b)15 feet of miscellaneous fill, peat and gray silt overlying a 10 footthick layer of medium to fine loose sand (N value about 12) overlyinganother 50 feet of red brown silty fine sand; (0) 10 to 15 feet of filloverlying l to 4 feet of peat and an underlying layer of loose sand of Nvalue 6 to 30.

The present invention also makes it possible to drive the pileaccurately in the desired direction. One factor in this is the presence,during driving, of the rigid mandrel within the socket which helps toinsure that the tip does not become deflected by localized variation insoil resistance, e.g. boulders, debris, uneven strata, etc. Anyappreciable deflection tendency will cause a portion of the inner wallof the socket to press hard against the corresponding outer wall of thesturdy rigid mandrel which will resist such deflection.

The particular tip size can of course be adjusted in accordance with thedesired load bearing capacity. Thus as between (a) a tip having a heightof 34 inches, and diameters of 20 inches at its base, and 24 inches atthe top on a 103 s inch diameter stern and (b) a tip having a height ofinches, and diameters of 23 inches at its base and 29 inches at the top,on a 12-% inch diameter stem, the load bearing capacity was higher forthe larger tip but the small tip is more economical to fabricate anddrive.

The piles of this invention are easily inspected and tested. Thus, ifthe tip should be seriously defective (e.g. cracked) this can be readilydetected since driving characteristics of the pile will be as if therewere no tip. The stem of the driven pile can be readily inspected byvisual methods before the concrete is poured into it.

It is understood that the foregoing detailed descrip' tion is givenmerely by way of illustration and that variations may be made thereinwithout departing from the spirit of the invention. The Abstract givenabove is merely for the convenience of technical searchers and is not tobe given any weight with respect to the scope of the invention.

I claim:

1. A method of producing a driven pile, which comprises attaching to atubular stem a tip of reinforced concrete having a larger diameter thansaid stern and having a central cavity aligned with said stem andadapted to receive the lower end of a pile driving mandrel, the base ofsaid central cavity being spaced above the base of said tip so thatbetween said bases there is a mass of the concrete of said tip, placinga pile driving mandrel within said stem with the lower end of saidmandrel within said cavity, driving said tip, to embed it in a bearinglayer, by the action of a pile driving hammer on said mandrel wherebysaid mass of concrete between said bases receives and transmits thepile-driving forces, removing said mandrel and pouring concrete intosaid stern whereby the poured concrete enters said cavity and extends upinto said stem forming a unitary body of hardened concrete joining saidtip and stem.

2. A method as in claim 11, said tip being tapered to increase indiameter from the bottom upwards, the maximum horizontal cross-sectionalarea of the tip being about 5 to 15 times the cross-sectional area ofthe stem, the taper being less than about 3 inches per foot and theaxial height of said tip being at least about 2 feet.

3. A method as in claim 2 in which the depth of said cavity is 3/ l to7/ of the axial height of the tip, and in which said cavity is linedwith thin corrugated tubular metal shell, said stem being of thincorrugated tubular metal shell whereby said poured concrete issurrounded by said corrugated metal shell within said cavity and withinsaid stem.

4. A method as in claim 1 in which said tubular stem is a thin metalshell incapable of withstanding the pile driving blows needed to forcesaid pile to its driven load carrying position and the tip having across-sectional area which is at least twice, and up to times, thecross-sectional area of the stem.

5. A method as in claim 1 in which said pile is driven until theresistance to the driving force indicates that the desired load bearingcapacity is attained, said bearing layer being loose granular soilhaving an N value of less than 30.

6. A method as in claim 4, in which said pile is driven until theresistance to the driving force indicates that the desired load bearingcapacity is attained, said bearing layer being loose granular soilhaving an N value of less than 30, said tip being tapered to increase indiameter from the bottom upwards, the maximum horizontal cross-sectionalarea of the tip being about 5 to 15 times the cross-sectional area ofthe stem, the taper being less than about 3 inches per foot and theaxial height of said tip being at least about 2 feet, the depth of saidcavity being 3/l0 to 7/10 of the axial height of the tip, said pouredconcrete is surrounded by said metal shell within said cavity and withinsaid stem, the axial height of said tip being less than one-third of theoverall height of said pile.

7. A method as in claim 4 in which said tip has a diameter of about 24inches at its base, a diameter of about 30 inches at the top, an axialheight of about 60 inches and a taper of about three-fifths inch perfoot and said stem has a diameter of about 14 inches, and the depth ofsaid socket is about 0.4 to 0.6 of the height of the tip, theground-engaging surfaces of said tip being of smooth concrete, said tiphaving a circular cross-section.

8. Process as in claim 1 in which said hammer is driven at 50 to 120blows per minute with a pile driving energy of above 15,000 foot poundsper blow.

9. A method as in claim 1 in which said cavity extends down, from alevel at which the horizontal crosssectional area of said tip issubstantially at its maximum, for a distance which is at leastthree-tenths of the axial height of the tip and less than seven-tenthsof that height, said cavity being lined with a central tubular linerrigidly embedded in the concrete of said tip, said mandrel extendinginto and having its lower portion housed in said cavity to align saidtip and stem during the driving of said pile, said liner and said stembeing of corrugated tubular metal.

10. A method as in claim 9 in which said unitary body of hardenedconcrete is in contact with, and conforms to, the corrugations of saidliner and said stem and said hammer is driven at 50 to 120 blows perminute with a pile driving energy of above 15,000 foot pounds per blow,and in which the pile is driven until the resistance to the drivingforce indicates that there is adequate load bearing capacity, said loosegranular soil having an N value of less than 30.

11. A load-carrying pile in place in the ground, comprising a metal tubeattached to a tip of pre-cast reinforced concrete having a substantiallyflat base and a central cavity aligned with said tube, said tubeextending into said cavity, the base of said central cavity being spacedabove the base of said tip so that between said bases there is a mass ofthe concrete of said tip of sufficient strength to receive and transmitthe pile-driving forces needed to force said tip and tube to the fullydriven load-carrying position, and a body of concrete, emplaced aftersaid tip and tube have been forced to said position, filling said cavityand extending up into said tube above said tip, said body having astructure unstressed by said driving, said tip being tapered to increasein diameter from the bottom upwards, the maximum horizontalcross-sectional area of the tip being at least twice, and up to 15times, the cross-sectional area of the tube, the taper being less thanabout 3 inches per foot and the axial height of said tip being at leastabout 2 feet, said pile extending through non-bearing soil to a bearinglayer of loose, granular soil, said layer having an N value less than30, said tip being embedded in said loose granular soil which has beencompressed by the driving of said tip thereinto.

12. A pile as in claim 11 in which said tube is incapable ofwithstanding the pile driving blows needed to force said pile to itsdriven load-carrying position.

13. A pile as in claim 12 in which said tube is of corrugated metalshell.

14. A pile as in claim 11 in which the base of said tip has a diameterof at least 8 inches, and the depth of said cavity is at leastthree-tenths and less than seven-tenths of the axial height of said tip.

15. A pile as in claim 11 in which the axial height of said tip is lessthan one-third of the overall height of said pile.

16. A pile as in claim 12 in which the base of said tip has a diameterof at least 8 inches, and the depth of said cavity is at leastthree-tenths and less than seven-tenths of the axial height of said tip,and the axial height of said tip is less than one-third of the overallheight of said pile.

17. A pile as in claim 16 in which said tip has a diameter of about 24inches at its base, a diameter of about 30 inches at the top, an axialheight of about 60 inches and a taper of about three-fifths inch perfoot and said tube has a diameter of about 14 inches, and the depth ofsaid socket is about 0.4 to 0.6 of the height of the tip, theground-engaging surfaces of said tip being of smooth concrete, said tiphaving a circular crosssection.

18. A pile as in claim 11 in which said cavity has a depth of 3/10 to7/10 of the axial height of said tip, the depth being measured downwardfrom the level at which the horizontal cross section of the tip reachesits maximum.

19. A method of producing a driven pile, which comprises attaching to atubular stem a tip of reinforced concrete having a larger diameter thansaid stem and having a central cavity aligned with said stem and adaptedto receive the lower end of a pile driving member extending down throughsaid stem, the base of said central cavity being spaced above the baseof said tip so that between said bases there is a mass of the concreteof said tip, placing a pile driving member within said stem with thelower end of said member within said cavity, driving said tip, to embedit in a bearing layer,

Ml foot and the axial height of said tip being at least about 2 feet.

20. Process as in claim 19, said cavity having a depth of at leastthree-tenths of the axial height of said tip, said depth being measureddownward from the level at which the horizontal cross section of the tipis a maximum.

1. A method of producing a driven pile, which comprises attaching to atubular stem a tip of reinforced concrete having a larger diameter thansaid stem and having a central cavity aligned with said stem and adaptedto receive the lower end of a pile driving mandrel, the base of saidcentral cavity being spaced above the base of said tip so that betweensaid bases there is a mass of the concrete of said tip, placing a piledriving mandrel within said stem with the lower end of said mandrelwithin said cavity, driving said tip, to embed it in a bearing layer, bythe action of a pile driving hammer on said mandrel whereby said mass ofconcrete between said bases receives and transmits the pile-drivingforces, removing said mandrel and pouring concrete into said stemwhereby the poured concrete enters said cavity and extends up into saidstem forming a unitary body of hardened concrete joining said tip andstem.
 2. A method as in claim 1, said tip being tapered to increase indiameter from the bottom upwards, the maximum horizontal cross-sectionalarea of the tip being about 5 to 15 times the cross-sectional area ofthe stem, the taper being less than about 3 inches per foot and theaxial height of said tip being at least about 2 feet.
 3. A method as inclaim 2 in which the depth of said cavity is 3/10 to 7/10 of the axialheight of the tip, and in which said cavity is lined with thincorrugated tubular metal shell, said stem being of thin corrugatedtubular metal shell whereby said poured concrete is surrounded by saidcorrugated metal shell within said cavity and within said stem.
 4. Amethod as in claim 1 in which said tubular stem is a thin metal shellincapable of withstanding the pile driving blows needed to force saidpile to its driven load carrying position and the tip having across-sectional area which is at least twice, and up to 15 times, thecross-sectional area of the stem.
 5. A method as in claim 1 in whichsaid pile is driven until the resistance to the driving force indicatesthat the desired load bearing capacity is attained, said bearing layerbeing loose granular soil having an N value of less than
 30. 6. A methodas in claim 4, in which said pile is driven until the resistance to thedriving force indicates that the desired load bearing capacity isattained, said bearing layer being loose granular soil having an N valueof less than 30, said tip being tapered to increase in diameter from thebottom upwards, the maximum horizontal cross-sectional area of the tipbeing about 5 to 15 times the cross-sectional area of the stem, thetaper being less than about 3 inches per foot and the axial height ofsaid tip being at least about 2 feet, the depth of said cavity being3/10 to 7/10 of the axial height of the tip, said poured concrete issurrounded by said metal shell within said cavity and within said stem,the axial height of said tip being less than one-third of the overallheight of said pile.
 7. A method as in claim 4 in which said tip has adiameter of about 24 inches at its base, a diameter of about 30 inchesat the top, an axial height of about 60 inches and a taper of aboutthree-fifths inch per foot and said stem has a diameter of about 14inches, and the depth of said socket is about 0.4 to 0.6 of the heightof the tip, the ground-engaging surfaces of said tip being of smoothconcrete, said tip having a circular cross-section.
 8. Process as inclaim 1 in which said hammer is driven at 50 to 120 blows per minutewith a pile driving energy of above 15,000 foot pounds per blow.
 9. Amethod as in claim 1 in which said cavity extends down, from a level atwhich the horizontal cross-sectional area of said tip is substantiallyat its maximum, for a distance which is at least three-tenths of theaxial height of the tip and less than seven-tenths of that height, saidcavity being lined with a central tubular liner rigidly embedded in theconcrete of said tip, said mandrel extending into and having its lowerportion housed in said cavity to align said tip and stem during thedriving of said pile, said liner and said stem being of corrugatedtubular metal.
 10. A method as in claim 9 in which said unitary body ofhardened concrete is in contact with, and conforms to, the corrugationsof said liner and said stem and said hammer is driven at 50 to 120 blowsper minute with a pile driving energy of above 15,000 foot pounds perblow, and in which the pile is driven until the resistance to thedriving force indicates that there is adequate load bearing capacity,said loose granular soil having an N value of less than
 30. 11. Aload-carrying pile in place in the ground, comprising a metal tubeattached to a tip of pre-cast reinforced concrete having a substantiallyflat base and a central cavity aligned with said tube, said tubeextending into said cavity, the base of said central cavity being spacedabove the base of said tip so that between said bases there is a mass ofthe concrete of said tip of sufficient strength to receive and transmitthe pile-driving forces needed to force said tip and tube to the fullydriven load-carrying position, and a body of concrete, emplaced aftersaid tip and tube have been forced to said position, filling said cavityand extending up into said tube above said tip, said body having astructure unstressed by said driving, said tip being tapered to increasein diameter from the bottom upwards, the maximum horizontalcross-sectional area of the tip being at least twice, and up to 15times, the cross-sectional area of the tube, the taper being less thanabout 3 inches per foot and the axial height of said tip being at leastabout 2 feet, said pile extending through non-bearing soil to a bearinglayer of loose, granular soil, said layer having an N value less than30, said tip being embedded in said loose granular soil which has beencompressed by the driving of said tip thereinto.
 12. A pile as in claim11 in which said tube is incapable of withstanding the pile drivingblows needed to force said pile to its driven load-carrying position.13. A pile as in claim 12 in which said tube is of corrugated metalshell.
 14. A pile as in claim 11 in which the base of said tip has adiameter of at least 8 inches, and the depth of said cavity is at leastthree-tenths and less than seven-tenths of the axial height of said tip.15. A pile as in claim 11 in which the axial height of said tip is lessthan one-third of the overall height of said pile.
 16. A pile as inclaim 12 in which the base of said tip has a diameter of at least 8inches, and the depth of said cavity is at least three-tenths and lessthan seven-tenths of the axial height of said tip, and the axial heightof said tip is less than one-third of the overall height of said pile.17. A pile as in claim 16 in which said tip has a diameter of about 24inches at its base, a diameter of about 30 inches at the top, an axialheight of about 60 inches and a taper of about three-fifths inch perfoot and said tube has a diameter of about 14 inches, and the depth ofsaid socket is about 0.4 to 0.6 of the height of the tip, theground-engaging surfaces of said tip being of smooth concrete, said tiphaving a circular cross-section.
 18. A pile as in claim 11 in which saidcavity has a depth of 3/10 to 7/10 of the axial height of said tip, thedepth being measured downward from the level at which the horizontalcross section of the tip reaches its maximum.
 19. A method of producinga driven pile, which comprises attaching to a tubular stem a tip ofreinforced concrete having a larger diameter than said stem and having acentral cavity aligned with said stem and adapted to receive the lowerend of a pile driving member extending down through said stem, the baseof said central cavity being spaced above the base of said tip so thatbetween said bases there is a mass of the concrete of said tip, placinga pile driving member within said stem with the lower end of said memberwithin said cavity, driving said tip, to embed it in a bearing layer, bythe action of pile driving forces transmitted by said member wherebysaid mass of concrete between said bases receives and transmits thepile-driving forces, removing said member and pouring concrete into saidstem whereby the poured concrete enters said cavity and extends up intosaid stem forming a unitary body of hardened concrete joining said tipand stem, said tip being tapered to increase in diameter from the bottomupwards, the taper being less than about 3 inches per foot and the axialheight of said tip being at least about 2 feet.
 20. Process as in claim19, said cavity having a depth of at least three-tenths of the axialheight of said tip, said depth being measured downward from the level atwhich the horizontal cross section of the tip is a maximum.